Light-sensitive silver halide emulsions and process of making the same



Patented 25, 1928.

' UNITED STATES PATENT OFFICE.

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LIGHT-SENSITIVE SILVER HALIDE EMULSIONS AND PROCESS OF MAKING THE SAME.

No Drawing. Application filed Kay 16, 1927, Serial No. 191,928, andin'Germany May 20, 1926.

The present invention relates to light sensitive silver halide emulsionsand to a procass of making the same. Its object is to obtain valuablelightsensitive emulsions from foggy gelatines.

It is known that the ripening process is very important in themanufacture of sensitive silver halide emulsions. The sensitivenessattained thereby depends to a great extent on the qualities of thecolloid employed, for instance of the gelatin. The ripening capacity ofa gelatin may be enhanced by adding substances, the nature and quantityof which depends upon the kind of emulsifying process which is used.These substances are sulphur compounds of a certain constitution,ammonia and others. In this way it is possible to make use of badlyripening gelatin for producing emulsions of the highest sensitivity.

Many sorts of gelatin, however, cannot be used for making sensitivesilver halide emulsions because they produce fog before the emulsion hasripened to the sensitiveness desired. Such gelatins have not beenapplicable hitherto for the production of photographic silver halideemulsion, or they have had to be specially treated before use.

According to the present invention such unsuitable gelatins may be usedfor making clear emulsions of the highest sensitiveness by adding to theemulsion or to the materials from which it is made, one or moresubstances which prevent fogging. Appropriate additions for this purposeare certain products of decomposition of proteins which are sometimesincorporated in small quantity in the gelatin, e. g. hist-idine.Investigation has shown that the tendency towards fogging of many sortsof gelatin in the ripening process is due to the complete or partiallack of these substances which prevent fog. The gelatin may be enrichedduring its manufacture in its content of the efficacious substances orthese latter may be produced separately in order to serve as additionsto the colloid before the emulsion is made or to the emulsion in anystep of its manufacture or when it is poured on to the support of theemulsionlayer.

Not only the above-mentioned degradation products of proteins, forexample iminazolealanine, have been found to be suitable additions toemulsions forthe purpose in question, but generally iminazole and itsderivatives have proved to have an excellent fog preventing action.Their suitability for this purpose is probably dueto the fact that thehydrogen-atom of the imino-group can be exchanged for a silver-atom andthat adsorption compounds with the silver-salts of the emulsion areformed.

For example, a sensitive silver halide emulsion manufactured accordingto one of the known processes with a certain sort of gelatin showedconsiderable fog and little sensitivity. When there is added to thegelatin before or during the making of the emulsion or when the emulsionis poured on the support of the sensitive layer, 0.1-0.4 per cent ofnitrobenziminazole a clear and highly sensitive emulsion is obtained.

Having now particularly described and ascertained the nature of our saidinvent-ion and in what manner the same is to be performed, we declarethat what we claim is 1. Process of manufacturing light-sensitive silverhalide emulsions characterized by the step of incorporating in theemulsion a compound of the iminazole-series. 2. Process of manufacturinglight-sensitive silver halide emulsions characteized by the step ofincorporating in the emulsion a compound of the iminazole-seriesproduced by the degradation of proteins.

3. Process of manufacturing light-sensitive silver halide emulsionscharacterized by the step of enriching the colloid employed in itscontent of compounds of the. iminazoleseries.

4. Light-sensitive silver halide emulsions in which a compound of theiminazole-series halide emulsions in which colloids are incorporated thecontent of which of compounds of the in'iinazole-serics is enriched.

In testimony whereof we aflix our signatures.

PETER WULFF. BRUNO WENDT.

